Temperature compensated variable frequency oscillator



April 19, 1960 A. H. MACISZEWSKI ET 2,933,698

TEMPERATURE COMPENSATED VARIABLE FREQUENCY OSCILLATOR Original Filed May 13, 1954 United States Patent TENIPERATURE COMPENSATED VARIABLE FREQUENCY OSCILLATOR Arthur H. Maciszewski, Julius J. Hupert, Richard Goldstein, and Tadeusz Szubski, all of River Forest, 111., assignors to A.R.F. Products, Inc., River Forest, 11]., a corporation of Illinois 6 Claims. (31. 331- 176) sources are changes in temperature and variations in the AC. line voltage which supplies the power for the various power connections to the oscillator and associated circuits.

Accordingly, it is an important object of this invention to provide an improved means for compensating circuit changes caused by changes in temperature and particularly to provide an improved circuit for stabilizing the frequency of capacity tuned radio frequency oscillators.

In connection with the foregoing object, it is a further object of this invention to provide in such radio frequency oscillators complete two-point compensation of the frequency-temperature characteristic of the oscillator so that proper compensation is obtained in both low and high frequencies.

These and other objects and advantages of the invention are achieved by the signal generator illustrated in the accompanying drawing. In the drawings wherein like reference-numerals have been used to designate like parts throughout:

Fig. 1 is a circuit diagram, part diagrammatic, of the .variable radio frequency oscillator-of this invention and its connection with the reactor tube, the calibration oscillator, and the radio frequency output attenuator; and

Fig. 2 is a simplified circuit diagram of the temperature compensating circuit for stabilizing the frequency of the variable radio frequency oscillator. v

Referring now to the drawings and particularly to Fig. 1 there is shown the calibr'atediadio frequency section of the signal generator made according to and incorporating the principles of the present invention.- The calibrated radio frequency section of the signal generator comprises generally a calibrating oscillator 20, a harmonic generator and amplifier 22, a variable radio frequency oscillator 24 and a modulating or reactor tube circuit 26. In general the purpose of the calibrating oscillator is to generate an accurate radio frequency operating at a given fundamental frequency such as, for example, tw megacycles,

this frequency being calibrated and controlled to a high degree of accuracy. Theout-put of the calibrating oscillator 20 is then fed-to. the harmonic generator and amplifier 22 which generates harmonics of the fundamental frequency of two megacycles and amplifies these harmonic frequencies as well as the fundamentalfrequency to provide calibrating reference signals.

The oscillator 24 is continually variable over a specified range and as illustrated has five separate ranges over which 7, 2,933,698 Patented Apr. 19, 1960' ice ' which will provide the working signal to be used in test- Each element of the above radio frequency generating.

and calibrating circuit will now be discussed in detail.

Referring first to the calibrating oscillator 20, this oscil-- lator includes a duo-triode 28 whose operation is con-- trolled by a crystal 30. Although any suitable frequency of crystal 30 may be utilized, a crystal operating at a frequency of two megacycles is preferred. A crystaI operating at two megacycles permits one megacycle beat nulls to be generated with the use of a minimum of harmonics of the fundamental operating frequency of crystal 30. One of the terminals of crystal 30 is connected through a lead 32 to one of the cathodes 34 of tube 28 which is preferably a type 12AU7, and through a resistor 36 (820 ohms) to ground. The other terminal of crystal 30 is connected through a resistor 38 (820 ohms) to ground and through a resistor 40 (820 ohms) tothe other cathode 42 of tube 28. The cathodes 34 and 42 are heated by heaters 44 that are supplied with suitable power through line 46. One of the control grids 48 is grounded and the other control grid 50 is connected through a resistor 52 (4700 ohms) to ground and through a capacitor 54 (470 ,u if.) to one of the plates 56 of tube 28. The other plate 58 of tube 28 is connected through a line 60, an inductance 62 (0.9 ,uh.) and a shielded inductance 64 (0.9 h.) to a source 66 of high operating potential. A capacitor 68 (5000 ,uyf.) is connected from plate 58 to ground to filter out and prevent radio frequency oscillations from entering the power supply 66. Plate 56 is connected through a variable inductance 70 and a resistor 72 (1000 ohms) to line 60 whereby to provide a source of high operating potential for plate 56.

There is provided in parallel with inductor 70 a capacitor 74 (150 [.L/Lf.) and the junction'between inductance 70 and resistor 72 is connected to ground by another capacitor 76 (5000 (ll/ The above described circuit operates as a radio fre through a coupling capacitor 78 (470 ,u Lf.) from plate the frequencyv is continually variable. It is oscillator 24 56 to the first grid of a tube 80 which serves as the harmonic generator and amplifier for circuit 22. Tube 89 is preferablyfa pentode and may be for example a 6AH6 orany other 'pentode having similar characteristics. The input signal on the-control grid of tube 80 is developed across resistor 82 connected from the grid to ground, this resistor having a value of 47,006 ohms. The third or suppressor grid of tube 80 is connected directly to the cathode and the cathode is provided with self bias through a resistor 84 (220 ohms) which is connected to ground and which has in parallel therewith a capacitor 86 (5000 i f). The second or screen grid is connected through a resistor 88 (47,000 ohms) to a source of operating potential through inductors 62 and 64 and is bypassed to ground by-a capacitor 90 (5000 ,LL/Lf.)- The plate of tube 80 is connected through a resistor 92 in series with an inductor 94 which in turn is connected to a source of operating potential through an inductance '62 and 64. Resistor 92' preferably has a value of 400 ohms and inductor 94 is so chosen that the amplifier 92 tubes of circuits 24 and 26.

has a by-pass from two megacycles to and through 28 the operating range of the variable frequency oscillator 24 is to be in the range from zero megacycles up to and including '28 megacycles. If the range of the variable frequency oscillator 24 is to be greater or less, the values of resistor 92 and inductor 94 are chosen accordingly.

The sharp cut-oh characteristics of these circuit elements serve to give more accurate calibration.

The output from amplifier 22 will consist of an accurately controlled signal at two megacycles and the harmonics thereof up to and through the-14th harmonic which corresponds to 28 megacycles. The 15th harmonic and higher harmonics will be suppressed. The output of the amplifier 22 is fed through a pair of series coupling capacitors 96 (10 inf.) and 98 (1 ,nnf.) to the plate of the tube in reactor circuit 26;

'All of the operating potential for the tubes 28 and 80 and for the tubes in the oscillator circuit24 and the reactor circuit 26 are supplied from the. power supply or source generally designated by the numeral 66. The power supplied to power supply 66 is the usual 110 volts 6'0 cycle A.C. current which is supplied through a pair of lines 100 which will be hereafter referred to as the main supply line. The power supply 66, which is illustrated diagrammatically in Fig. 1, includes suitable transformers and rectifiers. One of the outputs of the power supply 66 is a non-regulated-63 volt heater supply, the terminals of which' are indicated by the numerals X" and Y? and are the source of current for the cathode heaters described above. The inductor 64 is connected to an unregulated voltage point within power supply 66 for supplying relatively high operating potentials to the plates and grids of tubes 28 and 80. Another output from power supply 66 is a 6.7 volt heater supply 101 which is used to heat the filaments of the tubes inoscillator circuit 24 and reactor circuit 26. V p e v One of the principal outputs of power supply 66 is an unregulated voltage appearing on line 102. Line 102 is connected to a resistor 104 (1600 ohms) which is in turn connected to a variable resistance 106 (1000 ohms). The movable arm 108 on the variable resistance 106 is connected to the plate of a voltage regulator tube 110 which may be of the type designated 0A2. The voltage appearing on arm 108 serves as a regulated voltage supplyfor use on certain of the grids and the plates in the The variable radio frequency.oscillator 24 utilizes aduo-triode 112 which may be of the type designated 61 6.

The cathode of tube 112 is heated by a filament 114 which;

is supplied with power from the low voltage supply 101. The cathode is grounded; the two control grids are connected to each other and the two plates are connected to each other. The grids are also connected to ground through a resistor 116 (33,000 ohms) and to a capacitor network which forms one of the tuning elements of the oscillator tank. More specifically, the grids are connccted to a capacitor 118 (82 ,u f.) which is in tUI'IICOH- nected to. a grounded variable capacitor 120 (12.4-77.6

to aresistance 142 (400 ohms) in series with an inductance 144. Inductance 144 is connected through "a line 146, inductance 148(14 ,u'n.) and an inductance 150 (14 uh.) to the arm 108 on which appears the'regulated high potential power supply.

The other terminal 152 of coil 134 is connected through a line 154 to the plate of tube 112 and accordingly the plate of tube 112 receives DC. potential through the coil 134. The plate of tube 112 isalso connected to ground through a series of-three parallel capacitors, namely a variable capacitor 156 (1.7-8.7 ,LLfLf-), a fixed capacitor 1 58 (10 net.) and another variable capacitor 160 (9.2-- 17.2 t). 7 V

Capacitors 120, 122, 124 and 160 are ganged together to maintain constant deviation sensitivity in the operationof the reactor tube 164 as the frequency of the oscillator'24 is varied, all of which explained in detail in applicants copending application, Serial 'No. 429,547, filed May 13, 1954, Patent No. 2,881,315 granted April 7, 1 959 for Multi-Band Compensated Oscillator. The described circuit 24 is operable to produce a continually variable frequency over a given range, there being several different individual ranges. More particularly, each coil coil 134. The output from the variable oscillator 24 is taken from the platethrough a line 162 to the plate ofa tube 164 in the reactor circuit 26. Tube 164 is preferably a 6AH6 pentode;

The cathode of tube 164 is heated by' a filament 166 which is supplied with potential from'the low voltage filament supply line 101. The third grid of the tube is con- .nected directly to the cathode and the cathode is in turn connected to ground through a resistance 168 (100 ohms). Cathode bias is provided for tube 164 by providing resistance 168 with a by-pass capacitor 170 800 out). i

The control grid of tube 164 is connected through a capacitor l72 (10 [Lil-f.) to the plate of tube 164 and to the plate of tub'e112 in the variable oscillator. The control grid of tube 164 is also connected to a suitable RL circuit generally designated by the numeral 174 which is in turn connected to a resistor 176 (470 ohms). Resistor 176 is connected to an inductance 178 (14 h.) and an inductance (14nh.) to a kilocycle deviation meter when calibrating and to a source of AF modulating voltage when desiredi; One end of resistance 176 is connected to ground through a capacitance 182 (470 with).

Instead'of the RL circuit 174, an RL circuit 174A, a resistance 174B, a resistance 174C; and a RC circuit 174D areprovided for use on different frequency ranges. The various circuit: elements 174174D are ganged to the coils 134' 134D so that these elements areaut'olmatically switched in both circuits when the trequency of oscillator frequency circuit-124 is changed.

The modulated orunrnodulated output from the'va'riable oscillator'24 is fed to a piece ofelectronic equipment to be testedi'by means of an output'radio frequency attenuator'generally designated by the numeral 191 in 'Fig. 1. The attenuator includes in general a pick-up coil' 192; one e'ndof. which is grounded as at 194 andthe other end.196 of which is connected. to the elec oscillator circuit 24 has five separate ranges and accordingly five separate coils 134 having identicalconnections but different circuit values .are provided. The center terminal 136 of coil 134 is connected through a line 138 to a resistor-140 (47 ohms) which is inturn connected ironic equipment to be'tested. Coil 192 is inductively coupled to the coil 134 in the tank circuit 24. An electrostatic shield 198 is provided to prevent excitation of thepick-up-loop or coil 192 by capacity coupling. The

pick-up coil 192 is positioned within mend" tube 200 so that'the tube, and coil'operate' onithe inductiye couplin'g mode asa wave guide below 'cutofi, V

A pick-up loop or monitor wire 202' is provided, the

lmonitor wire-extending intofthe'tube. 200 and being positioned between thepick-up loop'I9'2 and the electrostatic shield'198. Theposition of monitorloop 202 is adjustable; Aconnectionis made fi'om the .monitorldoj) 202 through a rectifier -204, a resistance 206, an inductance 208 and a second inductance 210 to a speaker. A capacitor 212 by-passes'resistance 206 to ground.

.Referring now to Fig. 2 there is shown a simplified wiring diagram of certain portions of the variable oscillator 24, the details of which are shown in Fig. 1 described above. The simplified schematic drawing of Fig. 2 will be utilized to explain the manner in which compensation for temperature variations are made in the new improved circuit.

Usually the frequency determining circuit elements such as inductance 134, capacitors 122-124, and capacitors 120 and 160 have a positive thermal coefi'icient thereby causing anegative frequency coetficient. This positive thermal or temperature coeflicient of the various frequency determining elements is counteracted in the present circuit by incorporating therein two capacitors having negative temperature coeflicients. These added capacitors having negative temperature coetficients are capacitors 126 and 158. It will be seen from Fig. 2 that the contribution of capacitor 126 towards compensating for thermal deviations is highest at the higher operating frequencies. Conversely the contribution of capacitor 158 toward correcting temperature deviation is greatest at the low operating frequencies. Accordingly capacitors 126 and 158 are effective to provide adequate negative temperature coefiicient contributions at both the high and low ends of the cooperating frequency range.

Capacitors 126 and 158 are preferably of a type using a ceramic dielectric, the dielectric material being chosen so that the capacitor has a negative temperature coefiicient. In certain instances it may be found that the frequency contributing components of an oscillator circuit have a negative temperature coefficient. In such cases capacitors 126 and 158 would be chosen to provide positive temperature coeflicient contributions.

This application is a division of the copending application Serial No. 429,547 filed May 13, 1954, for Multi- Band Compensated Oscillator, now Patent 2,881,315 issued April 7, 1959.

It will be seen that there has been provided a signal generator fulfilling all of the advantages and objects set forth above. Although certain specific examples and values of the circuit elements have been given for purposes of illustration, it is to be understood that various changes can be made therein without departing from the spirit and scope of the invention. Accordingly, the invention is to be limited only as set forth in the following claims.

We claim:

1. A temperature compensated variable frequency oscillator comprising an oscillator tube having a cathode and an anode, a variable frequency tuned series circuit including an inductance and a capacitance connected in series between said anode and said cathode to form an oscillator circuit, the frequency of said oscillator circuit normally changing in one direction when the temperature to which the oscillator circuit components are subjected increases, a first temperature compensating capacitor connected in parallel with a portion of the capacitance in said tuned circuit, and a second tcmperaure compensating capacitor interconnecting said anode and said cathode, one of said compensating capacitors compensating for temperature changes at relatively low operating frequencies and the other of said compensating capacitors compensating for temperature changes at relatively high operating frequencies.

2. A temperature compensated variable frequency oscillator comprising an oscillator'tube including an anode and a cathode, a variable frequency tuned series circuit including an inductance and'a capacitance connected in series between said anode and said cathode, the frequency of said oscillator normally decreasing when the temperature of the components thereof increases, a first temperature, compensating capacitor connected in par 'allel with a portion of the capacitance in said tuned circult, and a second temperature compensating capacitor connected between said anode and said cathode, each of said temperature compensating capacitors having a negative temperature coeflicient of capacity.

3. A temperature compensated variable frequency oscillator tunable over a predetermined frequency range, comprising an oscillator tube having a cathode and an anode, a variable frequency tuned series circuit including an inductance and a main tuning capacitance tunable over said predetermined frequency range, said inductance and capacitance being connected in series between said anode and said cathode to form an oscillator circuit, the frequency of said oscillator circuit normally changing in one direction when the temperature to which said oscillator circuit components are subjected increases, a first temperature compensating capacitor connected in parallel with said main tuning capacitance in said tuned circuit, and a second temperature compensating capacitor interconnecting said anode and said cathode, one of said compensating capacitors compensating for temperature changes over the lower portion of said predetermined frequency range and the other of said compensating capacitors compensating for temperature changes over the upper portion of said predetermined frequency range.

4. A temperature compensated variable frequency oscillator tunable over a predetermined frequency range, comprising an oscillator tube having a cathode and an anode,

a variable frequency tuned series circuit including an inductance and a main tuning capacitance tunable over said predetermined frequency range, said inductance and capacitance being connected in series between said anode and said cathode to form an oscillator circuit, the frequency of said oscillator circuit normally decreasing when the temperature to which the oscillator circuit components are subjected increases, a first temperature compensating capacitor connected in parallel with said main tuning capacitance in said tuned circuit, and a second temperature compensating capacitor interconnecting said anode and said cathode, each of said temperature compensating capacitors having a negative temperature coefficient of capacity, said first temperature compensating capacitor compensating for temperature changes over the upper portion of said predetermined frequency range and said second temperature compensating capacitor compensating for temperature changes over the lower portion of said predetermined frequency range.

5. A temperature compensated variable frequency oscillator tunable over a predetermined frequency range, comprising an oscillator tube having a cathode and an anode and a control grid, a variable frequency tuned series circuit including an inductance and a main tuning capacitance tunable over said predetermined frequency range and a compensating capacitance, said inductance and said capacitances being connected in series in the order named between said anode and said cathode to form an oscillator circuit, a coupling capacitance connecting said control grid to the junction between said tuning capacitance and said compensating capacitance, the frequency of said oscillator circuit normally changing in one direction when the temperature to which the oscillator circuit connecting said anode and said cathode, one of said fixed compensating capacitors compensating for temperature changes over the lower portion of said predetermined frequency range and the other of said compensating capacitors compensating for temperature changes over the upper portion of said predetermined frequency range.

6. A temperature compensated variable frequency oscillator tunable over a predetermined frequency range,

comprising an oscillator tube having a cathode and an anode and a control grid, a variable firequencymnedpensating capacitor interconnecting said anode "siid series circuit including an inductance and a main tuning icathode, each of said fixed temperature compensating-ca- :ca'pacitance' tunable over saidipredtermined frequency pacitors having a'negative temperatureeoeflicicnt of'carange and a compensating capacitance,- said inductance pacity, said first fixed temperature compensating caand said cap'acitances being connected in series in the 5 pacitor compensating for temperature'changesbver the order named between said anode and said cathode to dipper portion of said predetermined frequency range and form an oscillator circuit, a :coupling capacitanceconlsaid second fixed compensating capacitor compensating ,necting said control grid 'to the junction between said for temperature changes over the lower portion of said tuning capacitance and said compensating capacitance, predetermined frequency range.

the frequency of said oscillator circuit normally decreas- 10 1 ing when the temperature 'of the components thereof in- References Cited inthe file ofthis patent creases, a first fixed temperature compensating capacitor 7 UNITED STATES PATENTS connected in parallel with said main tuning capacitance v in said tuned circuit, and a second fixed temperature c'om- 2,231,389 Kofiyberg t..t-' c Feb. 1 1, 1941 

